text:
What are the differences between foward air controllers in US military?
US Military has forward air controllers that join the forces on the front line and help them communicate with aircraft on the battelfield.
I found several Wikipedia articles describing such position, but can't understand what are the differences between them.
https://en.wikipedia.org/wiki/Tactical_Air_Control_Party
https://en.wikipedia.org/wiki/Forward_air_control
https://en.wikipedia.org/wiki/Joint_terminal_attack_controller
https://en.wikipedia.org/wiki/United_States_Air_Force_Combat_Control_Team
https://en.wikipedia.org/wiki/United_States_Air_Force_Tactical_Air_Control_Party

As the descriptions in the Wikipedia articles mention, different branches and countries have different definitions. To make things more complicated meanings of the terms are overlapping and have changed over time. Most differences are in actual privileges of that role, but that also changes. From my point of view the most used term is JTAC nowadays.


text:
Are answers posted to the FAA Sample Knowledge Exams?
I'm studying for the private pilot knowledge exam, and wondering if the answers to the sample test are posted anywhere. Here is the exam: https://www.faa.gov/training_testing/testing/test_questions/media/PARSampleExam.pdf

I purchased the exam booklet (they have one edition for each year), which covers all the possible questions that might come up in the actual exam, with correct answers. My instructor told me that you can just memorize the answers from the question bank to pass the exam, since they're all MC questions. Of course that is not recommended!

I don't think this is true anymore with the new ACS, as far as I'm aware they no longer publish active test questions.

If that's the case, I think you can just purchase one for the exam a few years ago. Out of all the questions, I'd say at least 98% are unchanged the next year. That would provide you a reliable source for study.

Let me answer your question by first quoting from the 2017 Gleim Instrument Pilot Knowledge Test book.
The FAA no longer releases the complete database of test questions to the public. Instead, sample questions are released on the Airman Testing page of the FAA website on a quarterly basis.…
Gleim utilizes customer feedback and FAA publications to create additional sample questions that closely represent the topical coverage of each FAA knowledge test.
The rewrite removed questions that are no longer relevant to most pilots, e.g. NDBs, Colored airways, and added new questions on things like GPS, PFDs, CRM.
In addition, they now shuffle the answers for each tester, so you can’t just do things like remember that most of the answers to a group of questions is 'A'.
They supposedly cleaned up the answers on some of the calculation questions so that minor differences in measurement do not result in getting an answer that is not one of the choices. For example, in previous exams some of the charts were reproduced at 98% scale. If you didn’t correct for that you would get an answer that was midway between two selections.
They also cleaned up the questions that had two right answers but one was more right than the other.
Since the exams are testing for the same content, and draw the questions from known publications, understanding past questions will give you the knowledge to pass the current exam.
Purchasing a test book from GLeim, ASA, or Sporty’s is probably worth the money for most people. With your purchase, most booklet makers also give you on-line tests so you can go into the test well-prepared.
According to Gleim, 85% of test takers pass on the first try, so don’t make too big a deal out of the test. If you are prepared, you’ll pass.

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text:
Have airlines average fleet age been shrinking?
I had read somewhere that nowadays Average age of Airlines is shrinking. I do not know how much of that is true. I did see this -
https://simpleflying.com/airlines-youngest-fleets/
On the other hand, I read about some of the oldest fleets which have anywhere 15-19 years. There doesn't seem to be any data which gives any correlation if the age of the fleets has been shrinking or growing. I do know that having younger fleets means less-downtime and arguably better safety standards/record. Although, the latter is a mere speculation on my part. Does anybody know of any concrete data which says one or the other.
To make it more simple:
Is Average age of the fleets going up or down around the world?

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text:
Why didn't ejection seats become a thing in civil avation and only limited to military?
Recently, an Indian CDS Bipin Rawat and his family as well as eleven members of the Indian Army died in an helicopter crash. You can find the story here. I did look at any questions asked on the topic and found this which I guess is about a Russian helicopter.
While it perhaps is far more complex and expensive, couldn't today's VTOL aircraft as well as civil aviation aircraft have ejection seats ??? I do understand that the tailwind of a civil aircraft is an issue, but besides that, why haven't ejection seats played much more of a role in civil aviation and just limited to military aircraft ????

does any of these answer your question? https://aviation.stackexchange.com/q/52565/1467 https://aviation.stackexchange.com/q/9564/1467 https://aviation.stackexchange.com/q/49034/1467

The tailwind of a civil aircraft?

extreme expense, high danger for untrained user, and absolutely demands that a parachute be (correctly) worn as standard equipment.

Also worth reading: Are there any helicopters with ejection seats?

Plenty of answers to similar (but I would say not quite the same) questions deal with issues of cost - cost of ejection seats, lower payload capacity due to weight of ejection seats, cost of checking seats and parachutes on a regular basis, etc.
But there is another key issue: How useful would they be?
There is a big difference between military and civilian flying: war. Ejection seats are used in several different scenarios:

Damage due to war - missiles, guns, being chased "out of the sky". These things, hopefully, are extremely rare for civilian aircraft compared to military aircraft.
Test flights. Military aircraft are the ones that (generally speaking) push the limits on speed, altitude, etc. Plenty of pilots have ejected from military test flights.
Carrier landings. Scary when they work. Potentially fatal when they don't. A few feet off on land and you crash into grass before the runway or after the runway and have a chance to survive. A few feet off on a carrier and you are in the water and ejection is often the only realistic way to survive.
Air tanker refueling. Just one example of a dangerous activity routinely done by military aircraft and not by civilian aircraft where an accident can be deadly and ejection seats key to survival.

While most military flights are really just practice for war and not the real thing, the maneuvering involved and speed (except for the Concorde) are often quite different from civilian flights.
The end result is that the use case for ejection seats - the situations where it would be useful - is simply not the same for civilian aircraft.

Regarding #2 it is interesting to note that civilian test flights sometimes do have means for the crew to escape. For example, at least during early test flights of a new aircraft type, the test engineers and pilots wear parachutes, and the aircraft is modified to allow exiting it in mid-air. So, while not an ejection seat, there are escape systems used precisely in those situations you mention, even for civilian aircraft.

@JörgWMittag But even then, no ejection seats and I suspect the testing regimen is more "Will this fly?" than "What are the limits we can push it to?"

@JörgWMittag But even then, no ejection seats and I suspect the testing regimen is more "Will this fly?" than "What are the limits we can push it to?"

Somewhere in between, I would say. Normally, the limits would be part of the design criteria, but there definitely will be a "okay, but can we actually reach those limits, and what happens when we exceed them?" test as well. For example, wing bending is usually tested until the wing literally snaps in half, although in a test rig, of course, not in flight.

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How many thousands of flight hours does it take to certify a jetliner?
How much time in flight hours does it take for a civilian aircraft (the Airbus A350-1000 for example) to get its certification from say either FAA or EASA?
To make the question more practical, I used the example of the Airbus A350-1000. People could similarly use examples of Boeing or Comac (China, which I believe is currently going through certifications). I had read couple of articles where it was told/surmised that even though today's designers have far more complexity and far more parameters to check, the time to certification has been the same. I am not sure how much of that statement is correct or not. Can somebody help clarify or give some insight?

which type of hours are we comparing? flight hours? employee hours? calendar hours?

Closely related, perhaps a dupe?

To some extent, the actual hours spent on certification activities are trade secrets. You don't want to tell competitors how much sweat and tears it took you to get things going. And in the case of a certain manufacturer, some certification tasks have been handled as own work, which has been proven to be worth zero actual work hours.

I think this question is impossible to answer, even for the manufacturer. Much certification work is indistinguishable from the huge amount of design and testing that would have to be done anyway, so how should that be counted? Pondlife's link might be the best you'll be able to do.

Airbus states that both the A380 and the A350-900 initially required over 2,600 flight hours for EASA/FAA certification:

Airbus’ 21st century flagship A380 was certified by the two major international governing bodies – the European Union Aviation Safety Agency  (EASA) and the U.S. Federal Aviation Administration (FAA) – in December 2006, following a programme that began more than five years earlier and ultimately comprised more than 2,600 flight hours with a fleet of five test aircraft.
To ensure the A350 XWB’s reliability from the moment it entered commercial service in January 2015, Airbus implemented one of the most thorough test programmes ever developed for a jetliner. Lasting just over 14 months, an industry record, the A350-900 flight test and certification programme comprised a five-aircraft fleet that performed over 2,600 flight hours in total – with Type Certification received from EASA and FAA in September and November 2014, respectively.

(Airbus - Test programme and certification, emphasis mine)
The A350-1000 was certified after the A350-900 and required less flight hours for certification:

The Type certification is a requirement for the aircraft to enter commercial service. This milestone comes after an intensive flight test trials that have taken its airframe and systems beyond their design limits to ensure the aircraft successfully meets all airworthiness criteria. The three A350-1000 flight test aircraft powered by Rolls-Royce engines successfully accumulated over 1,600 flight hours.

(Airbus - Airbus A350-1000 receives EASA and FAA Type Certification, emphasis mine)


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What do I do with fuel, distance, and time to descend and climb, on nav log?
So I've got my navigation log mostly filled out. All that's left to do is determine fuel to climb and descend. I go to my Archer POH (Pilot Operating Handbook) and use the time, fuel, and distance to climb and descend charts. Got about 1.5 gal for both descent and climb. 8 min and 6 NM for climb, 8 min and 18 NM for descent. What do I do with these numbers?

Realize that both the climb and descent are taken from the en-route section.
I always calculate climb first and determine where I will reach top of climb on the sectional chart. I then calculate descent and figure out when I need to descend on the sectional chart. The distance in between is my en-route section.
From reading your question, it seems you calculated en-route from departure airport to destination airport. You don't want to do that.

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What are the names and the function of these aircraft components?

These images were taken from a Cessna 150 aircraft containing a Continental O-200 engine.

Related, in case you don't have all answers: C150 service manual. After 1976, this one.

Are you the pilot, owner or mechanic?

1 - nutplate holding something on the other side of the firewall
2 - starter or master contactor (a relay operated by low-current signal from cockpit switch)
4 - positive heavy-gauge cable to battery or starter
5 and 6 might be the alternator voltage regulator to hold the output voltage at 14.4V
10 - oil filter to remove carbon and other crud from oil
11 and 23 - magneto to provide carefully-timed high voltage pulses at for ignition
12 - alternator to charge battery and run electric instruments / radios
14 - vacuum pump to power gyroscopic flight instruments
15 - carburetor to meter air and fuel
21 - crankcase vent (?) to prevent blow-by gases from forcing oil out of the engine
22 - fuel strainer drain valve to drain water / crud from low point in fuel system
Better pictures would help to identify the other parts!

Are you sure it's a 12v (14.4) system and not a 28v one?

@RonBeyer C150s have 12V systems by design. I suppose someone could change out of r a 28V system if they really wanted to.

I believe 2 is specifically the starter solenoid. I believe the master solenoid is below the battery box.

1 - nutplate holding something on the other side of the firewall

2 - starter or master contactor (a relay operated by low-current signal from cockpit switch)

4 - positive heavy-gauge cable to battery or starter

5 and 6 might be the alternator voltage regulator to hold the output voltage at 14.4V

10 - oil filter to remove carbon and other crud from oil

11 and 23 - magneto to provide carefully-timed high voltage pulses at for ignition

12 - alternator to charge battery and run electric instruments / radios

14 - vacuum pump to power gyroscopic flight instruments

15 - carburetor to meter air and fuel

21 - crankcase vent (?) to prevent blow-by gases from forcing oil out of the engine

22 - fuel strainer drain valve to drain water / crud from low point in fuel system

And to fill in the missing items:
3 - Rubber nipple protecting the energize conductor for the item 1 contactor
6 - Over voltage sensor (shuts off alternator if voltage is too high)
7 - Vacuum hose to cockpit (feeds air powered instruments)
8 - Avionics cooling duct inlet.
9 - static pressure port.
13 - left side exhaust muffler / cabin heat exchanger.
16 - Induction air filter
17 - Induction air box including carb heat valve.
18 - Engine data plate.
19 - Spark plug.
20 - Air inlet for cabin heat system.
23 - Right magneto.
24 - Oil filler cap.
25 - Rubber nipple protecting battery positive wire terminal.
26 - Battery box.

I believe 6 is not an over-voltage sensor but the radio noise filter.

@JonathanWalters You are correct. Thanks

8 may be the AC system intake
9 is the static port for the pressure-based instruments
15 looks like a fuse box
18 is the engine information plate
19 is a spark plug

What kind of Cessna 150 has air conditioning?  Probably just cabin air intake

8 is an avionics vent intake; 15 is the Carburetor; 18 is more properly called the engine data plate;


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Up to what thrust setting of a gas turbine engine can the airplane stay stationary on ground?
I noticed that when a jet engine airplane is started or is conducting run-up, the airplane remains stationary even though the engine is already burning gas and is supposedly producing thrust.
What keeps the aircraft stationary while the engine is spinning? Up to how much percentage of the engine's maximum thrust can you put the thrust setting on as to not have the aircraft move about its stationary position?
An alternate question would be: "On what thrust setting on each engine (assuming twin engine) will the airplane start to move and accelerate?"

Brakes are holding aircraft from moving. Idle thrust is enough to taxi airplane. No idea about exact percentage.

Also note that flight idle will vary from airplane to airplane.

Burning fuel not necessary produce thrust. Up to 2/3 of engine power at full thrust is consumed by engine's compressor. So on idle this part is even higher. The rest is consumed by auxiliary equipment. So there is very little (if any) thrust available.

Depends entirely on how good the brakes are, and of course on how good the traction is.  On an icy ramp, your brakes might not have a lot of effect.  Also note that engines can be bolted down for testing.  If that can be done with the Saturn V's F1 engine, holding a commercial jet should be a piece of cake :-)

@jamesqf They don't actually bolt anything down during on-wing run-up tests, though, do they? I've never seen that done. Of course, when the engine isn't actually mated to an aircraft, then you need some kind of stationary stand to attach it to for a run-up test.

@reirab: Yeah, I was trying to make the point that you can always apply enough force to keep a plane, or a static-tested engine, from moving.  Whether it's an F1 on a test stand, or me forgetting to unhook the tail tiedown on my Cherokee is just a matter of degree.

@Eugene Taking air to burn produces bit of thrust alone. Piston engine produces noticeable thrust by it's inlet and exhaust even though it's not designed to. When fuel is burnt, the thrust is always there, better not to underestimate it.

@Agent_L Thanks, I see the point. You're right!

There are two answers to this question depending on how you look at it.
If the brakes are on: Full Thrust wont even move the plane this is a requirement of the braking system.
Brakes off: Somewhere a bit above idle. John covers it in his answer nicely. It will vary by loading and aircraft.
A propeller plane can get moving even at idle thrust. While jets don't do run ups (unless required for maintenance), propeller planes preform a run-up prior to takeoff where the brakes are utilized to hold the plane in place at a high thrust. A proper short field take off will also involve the application of brakes and full thrust.

I was writing the same. You could want to add that it is required also to perform engine run-ups.

This question seems to be about jets which dont do run ups but I will mention it in the prop context.

Well, jets DO do run-ups when required by maintenance.

Interesting I did not know that!

airports also have dedicated areas (and rules) for that, e.g.: https://www.portseattle.org/Environmental/Noise/Noise-Abatement/Pages/Aircraft-Engine-Run-ups.aspx

While the brakes can hold the aircraft during a run-up, it's important to follow procedures or bad things can happen as did with this A340 that crashed at Toulouse.

Anecdotally, I was told by a 757 captain (don't know what engines his model had) that when light, idle was all that was needed to start rolling and that sometimes they needed brakes to stop the aircraft from getting too fast when taxying.

One other assumption that you are making is that they are on a hard paved dry surface.  (watch out if there is ice!)

Are you trying to slide off on a tangent :)

I know the question's tags specify jet engine, but it is worth noting that for some turboprop designs the brakes will generally not hold the aircraft static when full power is set.

I very much doubt that the brakes are guaranteed to hold at full power. The maximum static braking force is very close to 1G, and there exist planes that can accelerate straight up.

@Joshua Only fighter jets and high-end aerobatic aircraft (well, and rockets) have anything close to thrust >= weight. Others are much less. 14 CFR 25.735(d) requires the parking brake to be able to hold the aircraft static at full power on one engine and max ground idle on all others. Part 25 is the airworthiness standards for transport-category airplanes.

I noticed that when a jet engine airplane is started or is conducting run-up, the airplane remains stationary even though the engine is already burning gas and is supposedly producing thrust.

The fact that the engine is burning gas does not necessarily mean that it is producing thrust. The extreme example of this is the Auxiliary Power Unit (APU), which is a jet turbine that never produces thrust, it only produces electrical power and hydraulic pressure.

What keeps the aircraft stationary while the engine is spinning?

Friction. Brakes. Tie-down ropes. Clamps. Anything.

Up to how much percentage of the engine's maximum thrust can you put the thrust setting on as to not have the aircraft move about its stationary position?

That depends on how firmly the airplane is held to the ground.
Here is an example of a 737 being pushed around purely by wind. In other words, in this case, the thrust needed to get the airplane moving is exactly 0.
For the other extreme, it is a certification requirement, that even at full thrust, the brakes must be able to hold the airplane (e.g. in case of a FADEC malfunction).
This is sort-of the opposite of what you asked for, but it demonstrates the enormous power of the brake system: as part of certification testing, the airplane must demonstrate a worst-case rejected take-off with

Maximum Take-Off Weight
Maximum Take-Off Speed
No Thrust-Reversers
Brakes completely worn-down
1 Brake completely disabled
5 minutes emergency response-time by firefighters

Note that in this case, the plane stops so fast that the engines don't even have time to fully spool down. So, not only are the brakes able to hold the airplane in place at full thrust, they can even stop it from high speeds at full thrust.
And really, this is pretty much true for all vehicles that use brakes. E.g. automobiles usually also have brakes that are more powerful than what the motor can put out. That's how you do burnouts, after all. In general, a (heavy) vehicle that is moving has more energy than the motor, so if the brakes can stop the moving vehicle, then they can also stop the standing one.

RAF Waddington. 1980. Dark night. Early in the morning. Winter, cold and raining.  A basically horrible night. Vulcan ground crew tired, cold and hungry getting the last aircraft airborne for night exercise.  All cleared to taxi away. 30% thrust. No movement. Maybe the tyres are a little flat spotted or stuck to the tarmac. 50%, no movement. OK, here we go, 70% thrust.  Big bang, nose jumps up a couple of feet and the aircraft lurches forward. We check and on the pan (ramp), was the remains of the nose leg tie down hook snapped in half by about 30,000 lbs of thrust. Luckily, no other damage.

If air is being accelerated through a turbine there is an amount of thrust being generated, even if it's very small/negligible.

Yes, Notts90 is correct. Also, in the case of an airliner, the idle thrust is not so negligible. My understanding is that quite a few of them need to brake occasionally to maintain a safe taxi speed at (ground) idle.

Gatwick, some time in the 1990s. I was a passenger on a 747 which aborted takeoff fairly late because of an engine problem indication (which turned out to be an instrument fault, not an engine fault!) The pilot applied excessive braking, stopped the plane on the runway but seized the brakes. Max thrust on the other 3 engines wouldn't move it. Result: Gatwick main runway blocked for 5 hours. (Amusingly, after 3 engines wouldn't budge it, some optimist decided to try a tow truck - not surprisingly that didn't work either)

It will vary with the airplane and the engine(s).
The Boeing 737-800 will sit quite happily in one place with the parking brake released and the engines at flight idle (20% N1).  She will also taxi slowly at 20% N1, if you bump the power up enough to overcome initial friction and get her moving, and then pull the power back down to flight idle.  (I've done this in a simulator.)  Usual procedure is to push the power up to about 30% N1, and then pull it back down to flight idle as soon as the airplane starts moving.
Standard practice, and it is on the checklists: if you are stopped, SET THE PARKING BRAKE.


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What does the extending the flaps do (or any high lift device) to the Rate-Of-Descent of an airplane?
I know that deploying flaps will increase both drag and lift, thus increasing L/D ratio. But how exactly does that correlate with the increase/decrease of the rate-of-descent?

Normally, deploying flaps will reduce L/D ratio due to more drag than lift contributions. Nothing’s as good for normal flying as a well-designed clean wing, aerodynamically...

Flaps reduce L/D.  The lift increase is not as much as the drag increase, and ratio of lift over drag goes down.  So if L/D flaps up is 12 and I am descending in a glide at X knots with a vertical speed of Y (Y being 1/12th of my forward speed), and I deploy flaps and L/D is now 8, and I'm still at X knots, vertical speed will be higher, with the glide angle now much steeper at 8:1 vs 12:1 (vertical speed will have increased from 1/12th to 1/8th of my forward speed).  I can reduce the descent rate, but for that I have to slow the airplane down but the new vertical descent rate rate will still be 1/8th of my reduced forward speed, which will generally still be higher than it was flaps up.

This statement is not generally true.  Lower flap settings, such as those used for takeoff, increase lift substantially at lower speeds but not drag.  Higher flaps settings usually create much more drag.

If that was true you would leave takeoff flap on all through the climb, since if, say, 10 degrees extension improves L/D, then I'll have a better climb rate with them out.  Or if my engine quits and I'm gliding for distance, I can increase my gliding distance by extending takeoff flap.  Not aware of many airplanes where that works.  The L-13 Blanik sailplane has flaps that only go out a few degrees and are used for thermaling and landing because they lower the sink rate slightly and allow a bit slower speed for turning/landing.  But if u are running between thermals at best L/D, they come in.

According to the FAA, lowering or extending flaps allows one to increase drag without an increase in speed.  This increases descent rate for a given speed.
One must be careful to consider what factors are held constant to evaluate the effect.  For example, one can lower flaps during level flight. This will result in a lower pitch attitude--since they produce more lift, less angle of attack is required.  If power/thrust is not increased, speed will decrease due to increased drag.
However, an aircraft flying at a constant speed will descend faster (higher rate of descent) if the flaps are extended compared to when they are not.

Your last statement is not correct. If you maintain your speed and lower the flaps, you will gain Lift and therefore gain Altitude.

@Hubschr, that last statement is absolutely correct. If you maintain speed and lower the flaps, the aircraft will accelerate up very briefly until the angle of attack reduces back to the previous lift. That makes the plane climb, but climbing requires power, so it'll promptly start losing speed, and with that the lift again, which will in turn make it accelerate down, until it regains the speed. Eventually, it will stabilize at higher rate of descent than without flaps—assuming you don't add power.

"If you maintain speed [...]" is not "[...] so it'll promptly start losing speed [...]"

@Hubschr, remember, it is a dynamic process. You initially do something (well, it's too fast for the speed to change yet anyway), but then the system forces something else anyway.

If your hold your Speed and Angle of Attack constant and deploy your flaps, you will gain Altitude. That means, that you can reduce your Speed OR your Angle of attack (or both), while maintaining your altitude constant.
So depending on what situation, Flaps does not have to increase/decrease your rate-of-descent. It is more an interaction between Flaps, angle of Attack and Speed.

The question kinda implies that the thing you don't touch is the power levers.

The questions says nothing about the power levelers...

I didn't say it says it, I said it implies it. Because it does not make any sense otherwise.


text:
Which is better a push fan, a pull fan or both
intricate examination of modern by pass jet engines is despite where it is mounted, they use a pull fan configuration to generate thrust, which set up the most efficient, a pull fan or a combination of both on a single engine?

I would say pull fan, as that is what most engines use.
https://en.wikipedia.org/wiki/Turbofan

Modern turbofans have either a large single-stage fan or a smaller fan with several stages. An early configuration combined a low-pressure turbine and fan in a single rear-mounted unit.
Aft-fan turbofan.
  One of the earliest turbofans was a derivative of the General Electric J79 turbojet, known as the CJ805-23, which featured an integrated aft fan/low-pressure (LP) turbine unit located in the turbojet exhaust jetpipe. Hot gas from the turbojet turbine exhaust expanded through the LP turbine, the fan blades being a radial extension of the turbine blades. This aft-fan configuration was later exploited in the General Electric GE36 UDF (propfan) demonstrator of the early 80s. One of the problems with the aft fan configuration is hot gas leakage from the LP turbine to the fan.

So perhaps fans in front can use less expensive material since they don't have to contend with hot exhause temperatures.


text:
Is bleed air for fuselage pressurization at altitude purified or sterile/ If so how is this done
I just saw in the news, The epidemic deadly airborne disease Ebola has started killing people once again in Africa.  Aircraft to and from the EU, the US and the rest of world fly over this deadly zone on a daily basis.  People driving in ANY Tesla Vehicle or the US presidents car enjoy breathing purified sterile air free of any bacteria, viruses, fungi or any disease causing micro organisms, because all the air entering the car if windows are closed is purified by a UV light purifier.
Is aircraft bleed air for pressurizing the fuselage purified and if so, what technology is used e.g UV light.  If not are there any plans for one such process and would it drain more fuel if implemented.
Finally do such viruses pose a danger to aircraft fly over an affected country's airspace?

Ebola is not airborne.

If the air over there is that contaminated, then human race will have a bigger problem to worry about.

@Sanchises it is if a carrier boards a plane!

Bleed air is hot compressed air and no germ can live through that.  Also there is no way any germ will get up to any altitude that a plane flies at.  As someone else pointed out Ebola is not airborne and is only spread through direct contact with a sick individual.
As a side note it is not really the aircraft air conditioning system that gets people sick on airplanes.  People get sick by sitting in a seat that a sick person sat it.  If someone who is sick sat in the same seat for several hours then the surfaces of the arm rest and tray table would be highly contaminated.  Although here again Ebola is only spread by direct contact since the virus doesn't live long outside the body.

You  don't need to sterilize incoming bleed air in flight, because the bleed being tapped from the compressor to feed the cabin is really hot, way above boiling, so whatever living thing was in it would be cooked anyway.
The problems with interior air quality is in the fact that most of the air in the cabin in flight is recirculated, the fuselage being a slightly leaky balloon.  The amount of fresh air inflow depends on the leakiness of the pressure hull and the amount of air let out by the pressurization system outflow valves based on the controller's programming.  Cert requirements set minimum amounts of fresh air inflow.
The biggest headache is controlling humidity.


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What is the difference between conventional VOR and Doppler VOR?
There are two types of VOR (VHF Omnidirectional Range) navigation beacons; the conventional VOR (CVOR) and the Doppler VOR (DVOR).
What are the differences between them? Specifically I would like to know:

Do they generate the same navigation signal?
Can they be used by the same receiver, or do VOR receivers need to be specially adapted to DVORs?
Is one more accurate than the other?
Is one more susceptible to interference than the other?

Short answer:
There are several types of conventional VORs using either rotating or static antennas. What they have in common is:

They are relatively compact.
Bearing is determined from a HF signal rotating 30 rounds per second.
They are very sensitive to multipath interference created by reflection on nearby obstacles, and must be located at isolated places. They are often used for airway beaconing.

There are also several types of Doppler VORs, single or double sideband:

They requires a large 14 m diameter circular array of antennas.
Bearing is determined from the Doppler effect created by scanning the array at 1,300 m/s.
They are less efficient, inactive antennas from the array absorb a significant part of the signal emitted from the active antennas, reducing the effective range.
They are less sensitive to multipath, and are easier to install at airfields. They are commonly used for runway approach.

Bearing is more accurate with a Doppler VOR unless the conventional VOR site neighborhood is exempt of obstructions.
That said both types have the same tolerances from an ICAO standpoint:

The transmitting elements must be accurate to 2°. Most stations are able transmit a signal with an accuracy better than 0.5°. A perfectly sited VOR could deliver this precision to the receivers.

However errors are mostly created by the environment, by reflection and other phenomena changing the signal phase, similarly to a mirror inverting left and right on its reflected image. When direct and reflected waves interfere, an error can be introduced. ICAO limits this error to 6.5° in the volume of service. In practical most VOR stations are well below this limit, possibly using Doppler VORs in most cluttered sites.

A word about these multipath errors: The direct wave propagates along the line of sight (LoS), but the transmitting antenna radiates in other directions. The corresponding rays can be reflected, diffracted and refracted by obstacles and reach the receiver antenna as indirect waves. This can be beneficial, e.g. it extends considerably the range beyond LoS. But waves travel different distances before reaching the receiver:

This means their phase is different on the receiver antenna. Interferences occur, and they change the signal amplitude.
In a volume called the first Fresnel ellipsoid (FE1), centered on the LoS, where the length difference cannot exceed $\small \lambda / 2$, $\small \lambda$ being the VOR carrier wavelength, interferences are constructive, amplitude is increased.

In the second Fresnel ellipsoid where the difference is between $\small \lambda / 2$ and $\small \lambda$, interferences are destructive, amplitude is decreased, and this continues with other multiples of $\small \lambda / 2$. However 80% of energy is in FE1, and the rest is mostly in FE2. Therefore when planning a radio link, only FE1 is taken into account. The ratio between the obstructed areas in FE1 and FE2 determines the ratio of energy with constructive interferences, thus when siting radio stations, at least 60% of FE1 is kept clear of obstacles.
This can be a challenge. For an aircraft at a distance of 20 NM from a VOR located on the airfield, flying at 1000 ft QFE, the radius of FE1 at the middle point of the link is 500 ft. The ellipsoid is already tangent to the ground in the best case, and therefore the ellipsoid between the VOR and this middle point is slightly obstructed.
Limiting VOR errors consist first in removing obstacles from FE1. However as multipath first impacts amplitude, it hits conventional VOR harder, as this type of VOR depends more on a amplitude accuracy.

VOR principles
A VOR receiver, regardless of the technology behind, receives two sine signals repeating 30 times per second: Reference and variable signals, and determines the bearing by solely measuring the difference between their phases.
From a carrier standpoint, only amplitude modulation is used, but to minimize a possible influence of one signal onto the other, the VOR station uses a subcarrier, which frequency is low (9,960 Hz) but significantly distant from 30 Hz. One phase value is conveyed by normally modulating the carrier in amplitude, the other by modulating the subcarrier in frequency. The subcarrier then modulates the carrier in amplitude.
In addition, two antenna systems are used:

The carrier and the reference are send on one or more omnidirectional antenna(s) and all receivers see the same reference phase at the same time.

The variable signal is sent appart to appear different for receivers at different bearings. The type of antenna used depends on the type of VOR.

As explained below, the variable signal is not created by actual modulation of the carrier, but by synthetic sidebands. Modulation and sidebands are anyway equivalent by Fourier transform. Amplitude modulation changes the amplitude of the carrier over time (time concept), but also creates symmetrical sidebands on each side of the carrier (spectral concept):

12 kHz carrier with 500 Hz AM. Sidebands are created at a distance of 500 Hz from the carrier
Conversely, creating carrier sidebands by some method is the same as modulating the carrier.
Phases are equal when the receiver is located north of the VOR (360°M), and show a difference increasing by one degree for each degree of bearing counted clockwise. Therefore the phase difference directly gives the bearing value.
C-VOR and D-VOR differ by how the variable phase is made different for receivers at different bearings. The method relies on amplitude for a conventional VOR and on frequency for a Doppler VOR.
Conventional VOR (C-VOR)
Technologies have changed a lot in the first decades. This explains why C-VOR descriptions also vary a lot, and sometimes contain mixed principles from different generations. Early generations used a rotating dipole to broadcast the variable signal, but they were soon replaced by static antennas or slots on a cylinder, making VOR more simple and less demanding on maintenance.
The static system once used two pairs of Alford loop antennas, more commonly two pairs of vertical antennas. While a vertical antenna radiates equally in all azimuths, a vertical pair tends to increase the field in directions perpendicular to the pair plane.

Conventional VOR antennas for a Thomson CSF TAH 511. Source: STNA
In the aerial above, four vertical tubes form two crossed pairs and the rings below and above the pairs are omnidirectional antennas. A polarizer at the top of the tubes prevents them from radiating in vertical polarization, to increase accuracy.
Reference signal
The reference information is FM embedded into a 9.96 kHz subcarrier ("10k subcarrier") with a modulation index (modulation depth in ICAO parlance) of 16, meaning the subcarrier frequency varies by +/- 480 Hz.
Variable signal
The variable signal is created by artificially creating the sidebands corresponding to the subcarrier. Each pair of antennas receives a HF signal:

Which frequency is f-30 Hz or f+30 Hz (sideband frequencies)
Which phase is proportional to the sine or the cosine of the reference angle. This aspect is explained shortly.

Pairs are directional, sidebands are sent at right angle (image below, left), creating two individual figure-of-eight radiation patterns (below center), themselves equivalent to a larger composite  figure-of-eight along the symmetry axis (below right):

Two phenomena occurs:

Sidebands interfere with the carrier sent on the ring antennas. The result is a cardioid field.

With phase modulated by sine and cosine of the reference angle, the cardioid rotates at 30 revs per second, the frequency of the reference. This is equivalent to a rotating antenna broadcasting a constant signal (the technology used on earlier VORs).

The cardioid EM field which constantly increases and decreases in strength at a given point in space as the pattern rotates is sensed by the receiver as a constant signal modulated in amplitude at 30 Hz, this amplitude variation represents the variable signal.
Bearing determination
Carrier, reference and variable signal sidebands create a spectrum the receiver sees as a whole:

This spectrum has all the characteristics of a HF carrier modulated in amplitude by a 30 Hz signal and a subcarrier at 9960 Hz, itself modulated in frequency by the reference. Phases are finally extracted from this HF wave and compared:

Doppler VOR (D-VOR)
This VOR consists in an array of about 50 fixed Alford loop antennas located on a 14 m circle. Two opposite antennas are activated at a time, and are electronically switched so the active antennas seem to be moving along the circle at 30 rounds per second.

Seen from the receiver one source is moving forward, the other is moving backward, at a linear velocity between -1,300 m/s and +1,300 m/s (Mach 4).

Principle of the Doppler VOR: The variable signal generation
A 110 MHz source moving between -1,300 and +1,300 m/s creates a Doppler shift between -480 Hz and +480 Hz. This value, consecutive to the selection of the appropriate array diameter, is the same than the 480 Hz FM swing of the C-VOR, making the D-VOR compatible.
Reference
The 30 Hz reference AM modulates the carrier which is sent in all directions by an antenna at the center of the circular array.
Variable signal
The actual perceived Doppler shift depends on the direction of the displacement relatively to the receiver, maximum when "side" antennas are activated, null when "front" and "rear" antennas are activated.
Thus all receivers see a frequency variation repeating 30 times per second, and starting at a time varying with their own bearing. This shift therefore can be used as the variable signal.
The repeating Doppler shift being undistinguishable from frequency modulation, the variable signal must be conveyed in FM. However it doesn't FM modulate the carrier, but the subcarrier to be compatible with the C-VOR. To achieve this:

Each active antenna of the array transmit a pure frequency corresponding to a sideband of the subcarrier: f-9.96 kHz and f+9.96 kHz, f being the VOR carrier frequency. When associated with the carrier sent from the central antenna, these sidebands represent a carrier AM modulated by the 9.96 kHz signal.

When antennas radiating their pure frequency are given their angular velocity of 30 rps by the scan, a cyclic Doppler shift between -480 Hz and +480 Hz is automatically added. This shift is equivalent to a FM modulation of the subcarrier by a 30 Hz signal.

Spectrum created
The composite spectrum is identical to a C-VOR spectrum, the C-VOR receiver is able to continue working.

D-VOR frequency spectrum
Receiver
A VOR receiver is looking for 30 Hz and 9.96 kHz signals. We deliver both: 30 Hz signal on the central antenna and 9.96 kHz on the directional scanned array. We had to switch reference and variable signal functions on the carrier because the variable signal is naturally produced as FM, and the FM signal goes on the subcarrier in the standard.
Because of this inversion, the phase values are also inverted, and the result is a wrong bearing angle computation: When the angle is +a, the computation gives -a. The remediation consists in scanning the D-VOR array in reverse direction (counter-clockwise) and generating an opposite Doppler shift.
Accuracy
Both types of VOR (and their different subtypes) are required by ICAO to produce a bearing with a ±2° tolerance. The D-VOR is better in this aspect because it’s easier to produce an accurate Doppler shift than to form a precise pattern with space modulation.
Once the signals are emitted, they are subject to reflection on terrain and obstacles. The final composite error at the receiver location cannot exceed ±6.5°, as ICAO limits the error according to a bent (slow variation) tolerance of ±3.5° relative to theoretical course and to a superimposed scalloping (rapid variation) of ±3°.
On this aspect, the D-VOR is also superior, the variable signal is FM modulated and less subject to multipath errors. The smaller C-VOR is difficult to run on airfields due to reflections on close obstacles, the large D-VOR must be used for terminal VOR. The C-VOR is rather used for enroute navigation and implanted on isolated sites.
Large counterpoises under the antennas limit the reflection problem, and when the site used to built the VOR is carefully selected, the operational accuracy can be far better than the ICAO requirements in a large part of the service volume.
Answer to specific questions
Do they generate the same navigation signal?
There are two differences:

The C-VOR actually sends two modulated signal to generates a cardioid interference pattern which when steered creates an apparent AM modulation. The D-VOR sends only “moving” unmodulated sidebands which create by Doppler effect an apparent FM modulation.

To maintain compatibility with C-VOR, the D-VOR reference signal must be sent in AM, and the scan done in reverse direction of the cardioid rotation.

Can they be used by the same receiver, or do VOR receivers need to be specially adapted to D-VORs?
The C-VOR receiver is used for D-VOR. It computes a phase difference which is wrong (opposed cosine), but because the array is scanned counter-clockwise, the correct bearing is infered.
Is one more accurate than the other?
Wikipedia states, but with no reference, and I’m assuming it’s for a D-VOR: “The predicted accuracy of the VOR system is ±1.4°. However, test data indicates that 99.94% of the time a VOR system has less than ±0.35° of error”.
The same article states about ICAO Annex 10 volume 1: “This document sets the worst case bearing accuracy performance on a Conventional VOR (C-VOR) to be ±4°. A Doppler VOR (D-VOR) is required to be ±1°”. But I can’t find these figures in the version I have.
Annex 10 and Doc 8071 volume 1 (testing procedures) rather give three tolerances:

A maximum VOR equipment signal error of ±2°
A radial bend tolerance of ±3.5° from the perfect course.
A radial scalloping error of ±3° around the bend.

The two last errors are due to the environment rather than to the instrument. VOR are located at places where these errors can be minimized.
So the acceptable total deviation of ±6.5°, as attested by Doc 8071 volume 1 §2.3.48, when the radial is bent by ±3.5° and a scalloping of ±3° is superimposed. However scalloping is a rapid oscillation around the course, and in most cases is ignored by the pilot who keeps working on a mean deviation value (but there are limitations of scalloping when the autopilot is used, because the A/P can react to oscillations).

ICAO VOR tolerances on bearing value
The D-VOR was designed to minimize the multipath effect, the variable signal is frequency modulated for this reason. The size of the counterpoise was increased so that reflection occurs on a controlled surface, rather than randomly. This way VOR could be located on airfields, allowing better VOR approaches and easier maintenance.
However D-VOR introduces a new error: The array antennas are close to each other, therefore the inactive antennas on each side of the active one interact on the signal. First they delay the wave, introducing an error in the phase before the wave is Doppler-shifted. Second they absorb a large portion of the energy, reducing the range. As explained, the 14 m diameter can't be changed to space further the antennas, and they cannot be spaced vertically without impacting the maximum elevation of the signals and increasing the cone of silence, which is already relatively large (100°).
Another error is the discretization of the bearing information due to a scan over only 46-50 antennas (the matter is complex), a fix is the so-called power blending: The two or four antennas around the active antenna are fed with a smaller power HF signal and the transition from one pair to the next is smoothed.
The last error, which has been partially corrected by the DSB D-VOR (the one with two sideband antennas described here) is related to the portion of counterpoise between the antenna and the receiver which varies with the antenna location. If a reflection occurs on the ground, and the one from the reference antenna occurs on the counterpoise, then their path is not equal and the phase difference is altered (however the modulation wavelength being 10,000 km, a path length error of 1 km is not very significant).
It's difficult to quantify a mean error, it really depends on the conditions the VOR is used and at which elevation angle the receiver operates. There are tools for simulation like the Ohio University Navaid Performance Prediction Model (OUNPPM) you may already know. Here is a study of the C-VOR/D-VOR accuracy with this tool.
Is one more susceptible to interference than the other?
For interference from signals or from obstacles, the C-VOR is more prone to errors because of the use of AM for the variable signal. In the D-VOR the reference is AM modulated, but a receiver can maintain a local reference using a PLL oscillator synchronized with the VOR reference when the signal is good, and reject transient spurious values (it’s like maintaining a local time reference, synchronized from time to time with a master clock).
Here is a study of wind turbines interference on D-VOR.
That said:

EUROCAE ED-52 provides a guidance for VOR siting.

For foreign signals, VOR are subject to a requirement from ICAO (Annnex 10, volume 1, §3.3.8.1): "The VOR receiving system shall provide adequate immunity to interference from two signal, third-order intermodulation products caused by VHF FM broadcast […]".

Excellent explanation. Thank you for taking the time to write this answer!

Indeed a very good explanation.(Way better than chatGPT could have done ;)) )     Would you mind sharing the sources of theses images and knowledge(if there are any of course)?

@n00b: Thanks a lot. For knowledge origin, can you be more specific in what you're interested in? Images are mine (mostly Inkscape), else source is indicated.

@mins Wow great images then :) to be more specific I was interested in this part: "The cardioid EM field which constantly increases and decreases in strength at a given point in space as the pattern rotates is sensed by the receiver as a constant signal modulated in amplitude at 30 Hz, this amplitude variation represents the variable signal." I do agree with this explanation, makes perfect sense to me, but some people don't agree and I believe I would need a stronger source to change their mind (not a "random" internet guy who is in the TOP0.3% :P)

@n00b: This part is explained in this video, starting at 23:40. The actual pattern is called a limaçon de Pascal, but is usually known as a cardoid (a similar curve which equation is actually slightly different). This CVOR signal should be easy to simulate in Matlab/Python for a convincing demo. I don't have a reference like a textbook unfortunately.


text:
An example of remotely controlled flight control surface?
I'm aware of hydraulic, mechanical, and electrical ways to control flight control surfaces on an aircraft, but are there any examples of control surfaces which are remotely controlled? Can you explain their working?
Also, will this system come under Remote Position Control (servomechanism), or is it something different?

Would RC models qualify?

Nope. Real commercial aircrafts.

By remote control do you mean wireless? I'd be extremely surprised if there was a case. Opens up hacking possibilities.

Hydraulic, mechanical, and electrical actuation already is remote control of control surfaces. Can you describe better what you have in mind? Do you mean wireless? Do you mean remote control from cockpit, or from ground?

I mean remote control from the cockpit. I have an assignment on Remote Position Control (the servo-mechanism topic in control engineering), and they are specifically asking for an aircraft's control surface which is controlled remotely, and then we have to explain the operation of this RPC (remote position controller).

@HoodedSilhouette98 No, really, what do you mean by "remotely controlled"? The control surfaces are controlled from the cockpit. They are not in the cockpit. Therefore, in the ordinary English langauge sense of the term, they are remotely controlled. What do you mean when you use the words "remotely controlled"?

"hydraulic, mechanical, and electrical" are power technologies for actuators possibly controlled by RPC. First it must be clarified if remote is related to the distance (or the media e.g. wire or radio) between pilot interface (or autopilot) and RPC or  between RPC and actuator. The only difference I can see is that the RPC must receive a feedback from the actuator in order to know its current position.

@DavidRicherby Yeah I understand that all flight controls are obviously controlled from the cockpit. At first I thought that maybe my assignment asks about wireless control of control surfaces like rudder. Upon second thought I feel that this is highly unlikely to happen, and maybe remote control just means staying in the cockpit and controlling. So here's the exact question:
Select an aircraft control surface that is controlled remotely, then explain the operation of this remote position controller

This in bold^ is all I've been asked @mins so it'd be great if you guys can help me out. Thanks.

From the bold extract, it seems the question boils down to "explain how a RPC works for a given control surface".

And how can we explain that? What is to be mentioned? Just the basic block diagram and a feedback loop? @mins

@HoodedSilhouette98 If you want clarification on what the exercise means, you should ask the person who actually set the exercise, not random people on the internet. We can't read their mind.


text:
What is the recommended pressure for refueling an Airbus A380?
What is the recommended pressure on the hose that refuels an Airbus A380 when fueling this aircraft? How many litres per minute does it pump into the tanks. Can it safely be increased to reduce fueling time?


text:
What is the 'fuel cost' of a pneumatic braking system vs. a hydraulic one, in terms of weight?
A pneumatic braking system has indisputable advantages over a hydraulic braking system for large and heavy aircraft in terms of braking force and secondary perhaps in terms of weight (pipes and hydraulic fluid). However it requires engine input to compress the air and generate the pressure and force required for braking, all of which use fuel.
What is the cost of a pneumatic braking system from a fuel point of view as opposed to hydraulic in relation to weight for a large Jumbo like the Airbus A380 or Boeing 747 if one had to consider using hydraulic brakes for any of these aircraft?

indisputable advantages<< I question this - if there were advantages then aircraft would be using pneumatic brakes, but they aren't. A pneumatic system off the engines usually runs at around 50psi, whereas a hydraulic system runs at either 3000psi or 5000psi - MUCH more effective for braking.

Negligible at most. An A380 flies at 100MW for dozens of hours per trip yet you care about a few KW for brake actuators that operates a few minutes or less per trip?

The fundamental issue is air is compressible which makes it more difficult to control. See: https://aviation.stackexchange.com/questions/21426/why-do-aircraft-use-hydraulics-instead-of-pneumatics

There is an existing triple redundant hydraulic system in those planes required used for the control surfaces. Those are not something you want controlled by pneumatics.
This means the weight of the compressor, buffer tank etc. is already there and using it for brakes means you only need to pull a line from a supply/return line (which would also be near the gear to actuate it anyway) and adding a servo valve.

Interestingly there is one example of this entering service and provides a decent reference point. The Fokker/Fairchild F-27 had an all pneumatic undercarriage (breaks, retract, and steering). When compared with similar aircraft (role/size/era) like the Hawker Siddeley HS 748 or the Handley Page Dart Herald the F-27 actually preformed a bit worse although that by no means indicates the brakes are the cause of this.
All told the system had a flaw in the early implementation:

I flew the FH227 on the DEW line in the early 70's. We operated from
  gravel strips to resupply the radar sites. A definite step up from the
  DC3's and the C46's.In warm weather (+20c or higher) we would from
  time to time use the water meth injection for t/o. The gear was
  pneumatically operated.If there was any moisture in the lines in the
  winter (-50c or lower),the gear could freeze in the up position.The
  company modified the system with a standby 3000 psi nitrogen bottle
  with a separate set of lines which could be used to lower the gear if
  this situation happened (only once that I know of).Operating in the
  arctic in shirt sleve comfort was a very nice experience.


text:
Who or what is the DEN and what do they do?
I was reading some older Av.SE pages and ended up on the ATC procedural document JO 7110.65 for handling emergencies. Down at the very bottom under 10.2.19(b) which has to do with medical/health emergencies, it instructs 'essentially the ATC location manager' to contact the DEN.

b. The OMIC/OS/CIC must relay the information to the DEN as soon as possible.

Who or what is the DEN and what do they do?
Because DEN is such a general three letter acronym searching for it gives me lots of hits for the Denver airport and I don't think that is a likely answer because who would they call?

From FAA JO 7210.3:1

21−4−1. DOMESTIC EVENTS NETWORK (DEN)
a. Domestic Event Network (DEN). A 24/7 FAA sponsored telephonic conference call network (recorded) that includes all of the air route traffic control centers (ARTCC) in the United States. It also includes various other Governmental agencies that monitor the DEN. The purpose of the DEN is to provide timely notification to the appropriate authority that there is an emerging air−related problem or incident.
b. Required ATC facility DEN participation.

All ARTCCs.
All facilities in the National Capital Region (NCR).
Approach control facilities must participate on the DEN during President of the United States (POTUS) TFRs, National Special Security Events (NSSE) affecting their area, or when directed by System Operations Security or the DEN Air Traffic Security Coordinator (ATSC).
ATCT must participate on the DEN during arrival and departure phase of POTUS, Vice President of the United States (VPOTUS), First Lady of the United States (FLOTUS) movements, or when directed by System Operations Security or the DEN ATSC.
If the ATC facility is not actively monitoring the DEN or have a dedicated line to the DEN, they should call into the DEN directly via [redacted].
All communication regarding real−time security concerns and operational impacts should be initiated and coordinated on the DEN. The premise of the DEN is a need to share versus a need to know.
The DEN is an open mode of communication and is not intended for classified information.

The DEN was established in the aftermath of 9/11 to provide an "always-open" line of communication between FAA HQ, ARTCCs, and other relevant agencies. Various events trigger reporting to the DEN, including but not limited to aircraft accidents, suspicious aircraft activity, and ATC facilities going ATC-Limited or ATC-Zero (inability to provide services).

1I would link directly to the HTML version of the order but it seems to be unavailable at the moment.


text:
How much of the landing runway is mine?
If I am cleared to land a couple of miles on final, may I use the entire runway to the departure end, or do I have to comply with "taxi instructions" the tower controller might give me like "turn right at taxiway foxtrot," while I am still concentrating on safely completing the landing? If he gives such a clearance, and I don't acknowledge for safety reasons, do I still have to comply? If I do acknowledge and do not comply, have I committed a clearance deviation? It's great to "help the guy behind me on final" but is this type of clearance even supposed to be given? If I slide off into the grass trying to comply with a clearance that has no relation to my landing calculations, who goofed up?

"If I slide off into the grass trying to comply with a clearance [...] who goofed up?" You did. You should be focused on landing and slowing down. Unless you've accepted a LAHSO, you can use the entire runway. Controllers should avoid giving you instructions while you are rolling out, but they often do. If a controller gives you an instruction you can't comply with, either a quick "unable" or just handle the aircraft and deal with the controller when you turn off.

This is really several questions jammed into one, it might be wise to wittle this down to one question, and then ask the remaining questions as individual questions.  They all seem to be worthy of their own answer.

ICAO 4.9 After landing -- Unless absolutely necessary, controllers should not give taxi instructions to pilots until the landing roll is completed. : Related

Related: http://aviation.stackexchange.com/questions/27215/is-it-a-flight-violation-to-mishear-atc-instructions-for-exiting-the-runway

Everything in Dave's answer is entirely correct.  To add to it, AIM 4-3-20 says:

The following procedures must be followed after landing and reaching taxi speed. Exit the runway without delay at the first available taxiway or on a taxiway as instructed by ATC.

(emphasis mine)
Controllers are not supposed to give pilots a turn off the runway until they've already reached taxi speed, but at busy airports, I've seen that rule stretched. You don't have to comply with any ATC instruction that you deem unsafe, but if you do and you slide off into the grass, it's your fault.

I'd be tempted to put the emphasis slightly different.  The part of that quote that stands out to me is "after landing and reaching taxi speed."  The fact that the next sentence does not apply until the speed is low enough seems like a really useful detail.

Concur. The runway is yours if you need it; if you require the full length to get down to taxi speed no one will call it a pilot deviation (though they might call your airmanship into question, depending on how long "full length" is). But once you do get to taxi speed, exit ASAP unless otherwise instructed.

If I am cleared to land a couple of miles on final, may I use the
  entire runway to the departure end, or do I have to comply with "taxi
  instructions" the tower controller might give me like "turn right at
  taxiway foxtrot," while I am still concentrating on safely completing
  the landing?

You generally will not get a taxi instruction until the controller sees the aircraft is on the ground. You have the whole runway available to you if you need it.

If he gives such a clearance, and I don't acknowledge for safety
  reasons, do I still have to comply?

As Ron mentions, you can always state unable.

It's great to "help the guy behind me on final" but is this type of
  clearance even supposed to be given? If I slide off into the grass
  trying to comply with a clearance that has no relation to my landing
  calculations, who goofed up?

This is an interesting question and will for sure warrant an investigation. As mentioned, you most likely won't be given a turn off until you are on the ground and the controller sees that. If you make an unsafe turn, that's your fault as PIC.
I will provide an interesting anecdotal story somewhat related to this:
When flying in a buddy's M20C, he knew that his hanger was at the far end of the 7000 ft. runway we were in-bound on. He, without informing the tower decided he would land long as he only needed a short distance. This would avoid un-needed taxi time, so he came in a bit high. The controller clearly assumed he was going to land short and would be off the runway sooner than we were, this in turn caused the controller to send the citation behind us on a go-around. There was no fault given to us as we technically had the whole runway to land. I assume the pilot of the citation was less than amused.

Ah, that useful runway behind you..

At LKPR you can have easily have a full airliner behind your C152. They usually give instructions to vacate via C (from RWY 24) well in advance and wouldn't like it if you missed it or turned too early and blocked another airline taxiing for departure.

An “antidote” is a cure for a poison :P What you have is an “anecdote.”

While it's tempting to take a high landing approach in that kind of situation, a sudden decrease in headwind can turn a "land long" into a "runway overrun". There is nothing so useless as the pavement behind you. If you are cleared to land, the runway is all yours - be safe and use it. The conscientious thing to do would have been to inform the controller and following traffic that he was going to use the whole runway, as long as it didn't interfere with safe operation of the plane.

The runway is yours and yours alone until you clear it one way or another. That doesn't mean you shouldn't clear it at the first available SAFE opportunity.
What happens when that rule is violated is shown time and again in runway incursion accidents, with the crash at Tenerife Sur between a KLM and a PanAm B747-200 being the tragic extreme (though that was a takeoff where another aircraft was still on the runway, unknown to the controllers and the aircraft taking off because of a breakdown in communications in dense fog).

The Tenerife disaster does not fit in as an example. None of the planes was landing. (KLM attempted to take off, Pan Am taxied for take off next after the KLM.) Further, the crash was caused by severe miscommunication, not by conscious disregard of priority rules.

@bogl it is an example of what can happen as a result of runway incursion, that's why I included it. And yes, there was a conscious disregard of the rules at least according to one report I read. It says ATC had ordered PanAm to take a specific taxiway to exit the runway, then assumed they'd done so when in fact PanAm had disregarded that instruction (the turnoff was at an angle they couldn't take) and failed to notify ATC of that, causing ATC (and KLM) to assume the runway was vacated when in fact it wasn't.

Yes, there certainly was and is a lot to learn from the Tenerife disaster, but how does it contribute to answer the QE's question?

@bogl as a reason for ATC to not allow an aircraft to enter the runway while another one is on it, for whatever reason. Before it it was common for ATC to give one aircraft permission to line up while another aircraft was landing long (usually while rolling out after touchdown), Tenerife caused that practice to be abandoned worldwide.

Two logic problems: (a) a rule that does not exist (yet) cannot be violated. (b) the question as well as your explanation in the previous comment is about landing, while in Tenerife nobody was landing.

USAir Flight 1493 might make a better example.

-1 Tenerife is completely irrelevant. The question isn't about take-off and it isn't about runway incursions.

@jwenting: a) because of the dense fog shrouding the airport, the Pan Am crew never saw the third taxiway, and, thus, thought that the fourth one (the one they were trying to turn off onto when the collision occurred) was actually the third one; b) they did try to notify ATC, but their radio transmission happened to come just as ATC radioed the KLM crew on the same frequency, which resulted in all but the first word of the ATC transmission - as well as the entire simultaneous Pan Am transmission - being replaced by a shrill whine.

@Sean at least one account I read says the PanAm crew saw the third turnoff but decided to not take it because they deemed the turn to be too narrow for a 747, and then failed to apprise ATC of that decision. This supposedly happened well before the garbled transmissions caused by interference between the two aircraft's and ATC's simultaneous open mikes.

Aviate, Navigate, Communicate. In that order.
First, don't slide off into the grass. You are still aviating, even on the pavement.
Second, safely get the plane to where it needs to be. If that means that you take a later exit, so be it.
Third, and only third, communicate with the tower. After you've ensured that you're not sliding off into the grass or missing exits.

I concur that 'Unable' is your best bet. You are the Captain, not ATC. If you flip the aircraft turning too quickly, s/he'll press the crash button and pour another coffee whilst you burn to death. It's that simple.
Be aware that a 'safe' taxi speed is probably lower than you think it is. It's hard to judge because the ASI is little use. Any kind of 'fast' taxi may involve significant use of the flying controls, not just the brakes and steering. It's only necessary for military, bush and floatplane pilots (I've done a bit of all 3), they get taught how to do it, and it requires a lot of focus, which means you won't be chatting to ATC at the same time.
Best advice is that if you feel any significant shift of balance, then there are probably aerodynamic forces still on the aircraft, and you should slow down until there aren't. If you haven't used steering and/or brakes on the landing roll, then you should do a light test of them whilst still on the wide, straight flat thing, before trying to steer off onto the narrow, curved flat thing.

Controller here. "S/he'll press the crash button and pour another coffee whilst you burn to death." Do I really need to point out that this statement is incorrect?

A controller's directive is to provide safe, orderly, and expeditious traffic flow, in those priorities. If you need the entire runway to fly and land safely, they'll understand, as should any pilot in the pattern behind you.

authors: Vladimir F Героям слава


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How close can I fly to a bridge?
I want to take some pictures of a bridge. How close can my pilot get me?

You might be better off finding a drone operator if that's feasible. They seem to be taking over the market for aerial photography

If operating under VFR rules, which your pilot probably is if he's attempting to stop you actually hitting the bridge in question and allow you good enough visibility to take a photograph in the first place, the rules vary slightly by location.
The FAA regulations will be as follows (Note: all emphasis mine - indicating what I believe is the interpretation of your bridge)
:

An aircraft must maintain an altitude of 500 feet above the surface [and], the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

and

An aircraft must maintain an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft over any congested area of a city, town, or settlement

Also note that helicopter rules differ slightly.

Helicopters may be operated at less than the minimums prescribed in [the previous quoted sections] if the operation is conducted without hazard to persons or property on the surface.

source: 14 CFR 91.119 - Minimum safe altitudes: General.
And the UK CAA rules are similar

An aircraft must not fly closer than 500 ft to any person, vessel, vehicle, building or structure.

and

[...] it must not fly less than 1000 ft above the highest fixed object within 600m of the aircraft.

So, in summary your pilot can get you within 500ft if it is an uncongested area, 1000ft if its a congested area - closer if he's got a helicopter and can do it without causing a hazard.

CAA rules for helicopters are not relaxed. A helicopter must not fly closer than 500 ft to any person, vessel, vehicle, building or structure except for the purposes of taking off or landing.

@Simon ok, bad wording. I took out the "relaxed" - but is my quote below that not an accurate summary of the Helicopter differences for VFR flight? (Ive added my source)

HI Jamie.  I wasn't critiquing, just adding info.  The CAA has no such variation.  Your answer is fine.


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What is the drag induced by a high bypass jet engine on an airliner?
What is the drag induced by a turbo bypass jet engine in a typical most modern airliner like the 777, the Jumbo Jet (Boeing 747-8) and the Airbus A380?
Given that the jet is travelling faster than the replacement of the air displaced by the engine suction, do parts in close proximity to this area where suction is largest cause less drag to the aircraft because of this micro second vaccum period occuring at all times when the aircraft is in cruise mid air?
I refer to turbo bypass engines because they are the ones most used because of fuel efficiency, noise, etc., in airliners, I do not ask about bypass ratio. I ask about the displaced air outside the engine, and the overall effect on drag caused by the engine as a physical component attached to the plane colliding with air.
Does the fact that it is sucking a very large amount of air around it reduce this drag and by how much compared to if it were not sucking any air at all?

I'm not asking about the bypass ratio and drag I'm asking about the engine as a physical part of the airframe, its close proximity to the displaced air by suction of the jet its under aerodynamics not drag and spinning parts like the propeller blades

Ok, I've voted to reopen after your edit. It's not a duplicate from what you explain.  However after it'll be reopened it may be closed again for unclear, so maybe you should try to improve/refine the question. Good luck.

The first line of your question is confusing - engines deliver thrust, the opposite of drag. The second paragraph further enhances the Huh? factor. The last paragraph does not seem to account for the fact that the aircraft is at cruising speed, and air is blown into it. I'm sorry but I have no clue what you're asking about.

@Koyovis Engines deliver net thrust. But it still makes sense to ask about drag caused by them, just as it makes sense to ask about the expenses of a profitable company.


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Would "wind turbine generators" in the bypass stream save fuel for jetliners?
What is the location of an aircraft's alternator, in a large airliner like a Boeing 747 or Airbus A380?
How much power does it produce in kilowatts?
And what is the possibility of installing it with fan blades? To act as a windmill/wind generator at the point where air is slowed down in a bypass turbo fan engine. I mean, incorporate it into the engine design so that it slows down the air to generate electricity, rather than using the motion of the engine.
The aim would be to reduce the amount of fuel required to generate electricity.

You mean something like a "Ram Air Turbine"? I have a feeling that using the residual power inside the engine is a lot more fuel efficient than the added drag from using a RAT all the time.

You don't get anything for nothing.  Since taking energy from the airflow to spin the turbine cannot be 100% efficient, then you lose more energy than you gain as you reduce the energy going into the engine from the airflow.  A direct geared drive is much more efficient (better than 99%) and uses fuel to generate the energy.

Related: Is it sensible to harness wind energy on an airplane?. The second paragraph of this question has been largely (if not exhaustively) addressed in the related question linked above.

When you write "so that it slows down the air to generate electricity, rather than using the motion of the engine", you mean converting airflow kinetic energy into electricity rather than converting mechanical energy of the engine. But you miss the airflow is itself created by the engine. So to use airflow, you need first to burn (additional) fuel to create a force, then convert this force into motion (relative airflow), then airflow energy into mechanical rotation using blades. These three steps are all imperfect. Using a shaft requires only the first step, so is more efficient.

The normal power generation is on the engines or the APU.  It may just be the light metal I fly, but normally I have starter-generators, with ratings like 28V -200ADC or 28V -300ADC. Typically the APUs have starter/generators.  One issue with alternators is the turbine rotational velocity is difficult to manage for frequency control. AC cannot be paralleled. There are numerous configurations, and they all seem different. Generally not driven with bleed air, which is used for starting.

As a rule of thumb from aircraft design, a windmilling propeller will require 10x the power extraction from the airflow to provide a certain amount of power to its output shaft (so 10 kW of power to the shaft requires 100kW of "flow power" that has to be made up through more thrust)

@mins my understanging of one of the functions of the fan in a turbo by pass engine is at the section of the fan where air enters the hot sections of th engine rather than the by pass section, at cruise, air is supersonic so the air is slovwed down by the fan, instead of using the engine's slow spin or fan motion to slow down the air why not install a turbine/ wind mill to generate electricit for other uses. to undestand this further, a ram jet uses cone to slow the air while a turbo by pas engine uses the fan

"air is supersonic [and must be slowed down, so] why not install a turbine/ wind mill [in the engine] to generate electricity". What matters is flow energy (a combination of speed and mass/pressure). What you suggest is less efficient than using the accessory box to drive the generator. In addition why would you risk having a broken blade in the engine case? When a wind turbine is available on an aircraft, its location is away from the engines, near the fuselage.

There are a few Alternators on big planes.
Most large aircraft have an APU which is often in the back of the aircraft. It is effectively a small turbine directly bolted to an alternator. It provides power while the plane is on the ground (and the engines are off) and can also be used in flight if need be to supplement the main system or in the event of a main engine failure.
The engine alternators are generally mounted and driven directly by the turbine (via a transmission) in this case near the compressor stage. You can read more in this thread and check out this video for a nice overview/explanation of jet accessory drives. You can also see where in this picture,

(source)
As mentioned in the comments you can have a Ram Air Turbine driven by airflow but these are presumably not as efficient as directly mounting it to the engine.

Large airlines DO have a wind vane turbine driven alternator that is deployed under emergency conditions, i.e. total engine / normal electrical system failure. The device also generates hydraulic pressure.

They are called Ram air turbines, or RAT for short.
Video: 747 RAT Test bed
These devices have saved many a flight. Most noticeably the Gimli Glider. A Boeing 767-233 that ran out of fuel, due to a math error, mid-flight over Canada in 1983.

Math error.  That's what I'll start telling the AAA guy when I run my car out of gas...


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Do aircraft tyres have inner tubes?
Do aircraft tyres have inner tubes? Modern small single-engine turboprops to the largest Jumbos. If not, did they ever have inner tubes? And if so, why were they discontinued?

They are tubeless.
Why? for the same reasons we have tubeless tyres on our cars.

Punctures are slower. A nail or similar which penetrates the tyre will itself form a plug.
Tubed tyres can handle high speed. Friction between the tyre and tube will causes failure due to heat.
Low pressure in a tubed tyre will quickly escalate into a flat as tubes only work well when properly inflated.
Tyres can move along the rim. You often see index marks in the rim matched to similar marks on the tyre. Not good on a tubeless tyre but really bad on a tubed tyre as this will stress the valve area.

Not true that all aircraft have tubeless tires.  Many have tires with inner tubes.  While I don't know about commercial airliners, many GA planes have wheels which actually separate into two halves by undoing a few bolts, like this: https://www.ebay.com/i/232441503859?rt=nc

All of our GA planes and light jets have innertubes.


text:
What happens if full thrust is applied at cruise altitude for 5-10 minutes on a 787?
What happens when you apply full throttle to the engines of a Boeing 787 at cruise altitude for 5-10 minutes?
Other than wasting fuel, what maximum speeds are reached?
Does that pose any danger or damage to the airframe?


text:
What Oil thickness is used for the geared turbofan jet engine gearbox
In light of the huge operating speed of the geared tubofan gearbox gearing down the fan speed, what Oil thickness is used for the geared turbofan jet engine gearbox and does it use use regular gearbox oil used in cars and trucks, also in light of the huge difference in operating speeds of these gearboxes?

The more regular specification for such oils is given for the viscosity in centistokes versus temperature, as an example the Mobil Jet™ Oil 387 lubricant that can be used on Pratt & Whitney PurePower® Geared Turbofan™ PW1900G engines has a viscosity of about 5 cSt at 100°C, and about 25cSt at 40°C
Other parameters are extremely important such as the flash point temperature, the fire point temperature and the autogenous ignition temperature
Also the Total Acid Number is an important parameter for engines oil.
Please refer to the following website for more details about above mentioned oil specifications.
https://www.exxonmobil.com/english-US/Aviation/pds/GLXXMobil-Jet-Oil-387

Thank you for the answer

I don't think oils for this application are classified by weight. The specification for Mobil Jet Oil II, for example, which is one of the approved lubricants for this application, is quite a bit more complex.

Thanks for the answer


text:
What is the operating temperature of a turbofan engine, and how is it kept at that temperature?
What is the operating temperature of a turbofan engine?
If advancements were made to materials through material science for the internal components would increasing the operating temperature result in better fuel efficiencies, better thrust and optimal engine performance?
How is the jet engine cooled to operate at the desired temperature?

There are various questions about jet engine cooling and a few about materials already…

You should consider splitting this into multiple questions. You are asking at least three questions at once here.

Q1: Assuming that by operating temperature you mean turbine inlet temperature, this article says the Pratt & Whitney F135 engine in the F-35 (JSF) has a TIT of 3600 °F (1982 °C / 2255 K), but that most high performance aircraft engines do not exceed 3000 °F (1649 °C / 1922 K), while non aviation engines are nearer 2700 °F (1482 °C / 1755 K) or lower. Exact figures for modern engines are very unlikely to be stated in public. Mattingly, in his book "Elements of Propulsion: Gas Turbines and Rockets" has a table (6-2, P363) that gives a general guideline, depending on the age of the engine. He says:

1955-1965 2000 °R = 1540 °F (838 °C / 1111 K)
1965-1985 2500 °R = 2040 °F (1116 °C / 1389 K)
1985-2005 3200 °R = 2740 °F (1504 °C / 1778 K)
2005-2025 3600 °R = 3140 °F (1726 °C / 2000 K)

The GE J79 gas turbine which had its first run in 1954 is claimed to have a TIT of 1710 °F (932 °C / 1205 K), so these guidelines look reasonable.
Q2: Increasing the turbine inlet temperature allows more fuel to be added, which increases thrust and hence thrust to weight ratio, and specific thrust (thrust per lb of air ingested). Increasing TIT (at the same pressure ratio) also has some effect on improving the specific fuel consumption. At the same TIT, SFC is improved by increasing the compressor pressure ratio. The chart below shows the effects for a particular engine, the specific effects  will differ for each engine depending on the bypass ratio etc.

Q3: There are three methods that can be used to cool turbine parts. The primary approach is to bleed off a portion of the compressor exit air, which then bypasses the combustion, and is feed into the turbine vanes and blades. The below picture also includes some numbers for the % flow of compressor exit air that is used.

Other methods that are often used as well include the use of small holes over the blades and vane surfaces, through which the cooling flow emerges. This provides a film of cool air over the part, and is known as film cooling (left picture). On some more modern engines, thermal barrier coatings are also used (right picture). These are ceramic coatings that act as insultion of the base metal from the hot gas. Usually the TBC is added as an extra method to help gain additional part life. But sometimes, the TBC is needed to obtain the base life, and is then know as "prime reliant".

Consider mentioning the cycle efficiency for the explanation of better fuel efficiency.

Yes, if you could increase the combustion temperature in the hot section of a gas turbine, you could dramatically increase the efficiency of the engine.  The problem of course is finding materials which can sustain structural integrity in these regimes for long service lives and still contain the hot gas; we are currently at the thermal limits of existing materials.
The key problems here are:
Temperatures - gas turbine hot sections operate at 1600 °F (871 °C / 1144 K) all the way up to 2600 °F (1427 °C / 1700 K) for high performance military engines in order to yield high thrust or high useful work for a unit of fuel burned.  No known metals can survive these upper limits and still maintain high yield strengths.  It also causes great thermal expansion problems between non homogenous materials and coatings as well as oxidation and galvanic corrosion.
Stresses - the spools of a gas turbine can spin as fast as 40,000 rpm in the cases of high pressure compressors and high pressure turbines.  This creates tremendous centripetal loads on the blades and other components which they must be able to endure and not exceed the yield strength of the material.
Extended operation between servicing and reliability - the engine must survive these loads for several hundred cycles over a period of several thousand hours between major overhauls.  Redundancy as well as resistance to damage must be built into the design as well.  The consequences are grave; the trustworthiness and reliability of two gas turbines engines are all that separates a successful Seattle to Moscow polar flight in a 777 and 320 people freezing to death in the Arctic Ocean.
Historically gas turbine hot sections have been constructed from alloys of metals with high melting points and good yield strengths like nickel and cobalt of a very high purity.  Titanium and Molybdenum are also beginning to be used in this as well.  Additionally forming techniques such as single crystal casting are used to remove crystal grains from the material to improve its strength.  The blades ('buckets') of a high pressure turbine are also cast with channels in them and have fine holes laser drilled in their surface in order to take compressor bleed air and 'bathe' the boundary layer of the bucket with cooler air, effectively wrapping it in a cool gas blanket to protect it from the high temperature exhaust.
More exotic materials and techniques are being considered for this.  GEAE and P&W both are exploring the use of composite and ceramic blades in hot sections.  These offer high yield strengths at high temperatures but again pose challenges in terms of oxidation and thermal expansion problems.


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Sonic boom impediment to hypersonic passenger flight
Given that the ramjet and scram jet engines could achieve hypersonic flight, is sonic boom the major impediment to passenger hypersonic flight today?  If so, why is it that space shuttles could travel at speeds in the regions of Mach 25. How did they deal with sonic boom in relation to noise pollution on the ground what was so unique about their design given that there were many space shuttle fights.

also, note that Mach, through the speed of sound, is a function of temperature: the Shuttle was travelling at M25 where the temperature (and thus the speed of sound) was lower, giving a higher Mach number for the same airspeed.

The space shuttles kept most of their sonic booms over the oceans - fewer complaints that way.

@mins - I'd forgotten about people hearing the "double boom" when a shuttle landed.

Note that the Space Shuttle didn't accelerate to orbital speed until it was out of most of the atmosphere.  On reentry, it was not travelling at Mach 25, it was decelerating from that speed to the ~225 mph at which it touched down.  Then consider the size of the fuel tank required to boost it to orbit, and the thermal protection required for reentry - and what happens when that protection fails.


text:
How does an Airbus pilot decide whether to use HDG-V/S or TRK/FPA guidance?
The Flight Control Unit of modern Airbus aircraft has a pushbutton for selection of either

heading / vertical speed (HDG-V/S), or
track / flight path angle (TRK-FPA)

guidance for the Autopilot and Flight Director. I know in principle what these modes mean (i.e. difference of heading vs. track, or between vertical speed and flight path angle) and how the guidance on the Primary Flight Display changes from Pitch/Roll bars to the Flight Path Vector depending on the selected mode:

What I would like to ask is when is each mode used. How do pilots decide which guidance mode suits them most in a given situation? For example, is it related to

personal preference of the Pilot Flying?
specific flight phases or situation/circumstances?
procedures that require a certain selection?

It's mostly up to points 2 and 3 on your list rather than personal preference:
Note that most ATC instructions (beit on departure,cruise or initial approach) will ask of you to fly a specific heading and/or a specific climb rate (v/s). This makes the hdg/vs mode the 'standard' mode to be used durring flight. This is also the mode where the F/Ds provide an easy to use guidance for the pilots to follow.
The reason for this Hdg preference for ATC is beyond the scope of this question, and is quite a nice narative on how historically we arrived at using heading for separation, but I will say this much: imagine ATC software attempting to interpolate the track of two converging a/c , to determine minimum separation and/or collision conflicts. Now imagine there is (unkown to the atc) changing wind along route, and both a/c will change hdg to maintain proper ground track. The math required is mind-blowingly complicated...(because changing hdg will change time of arrival at intersection,etc )
Anyway, once you look at some final approaches you will see that there is usually a final approach Track and a (3deg usually) glide path angle posted on the chart. The reason is that being closer to the runway, you start to become a bit more interested in your path wrt to ground rather that wrt to other trafic.
TLDR
TRK-FPA, as part of normal operating procedures, is only used when flying the final part of a non-precision approach, and is usually engaged  about 1 NM before the FAF.
Mind you, it's use is not prohibited outside of that, just there is kinda little use for it.

Using track would probably still be simpler for ATC (for separation, altitude is better anyway, and for vectoring the controller has to estimate the wind). The problem is that until recently it was impossible for pilots, and most aircraft still don't have prominent display of track to use for vectoring.

actually, using constant track for two converging traffic is amazingly difficult to compute min separation. This is why ATC might temporarely give you a “continue on present heading” for a few minutes. Moving on a constant heading means that both aircraft are now moving together with the airmass, taking the wind (and wind change) out of the equation. Google it on the net, I was amazed how complex the equations are to compute the minimum separation of two aircraft

The standard-operating mode for lateral navigation is the NAV mode, where the aircraft is tracked inbound RNAV-Waypoints, heading mode is of no use because you would always have to correct for the wind. ATC clearances may assign a heading to the aircraft, then the HDG mode is used for lateral navigation, how would you fly that with the TRK & FPA mode with changing winds. Also vertically V/S is used rather than FPA. Flying a vertical speed (feet per minute) is a lot easier to handle to optimize your descent or climb profile. There are also other lateral and vertical modes used like CLIMB / OPEN CLIMB, DESCENT / OPEN DESCENT.
Only occasion TRK & FPA is used is during some Non-Precision Approaches to track Radials or Bearings and to fly a vertical Path (trajectory).
Selecting the TRK & FPA mode puts the "BIRD" on the PFD, with the Flight directors off and in manual flight this is a good aid (showing you the actual trajectory of the aircraft) for flying raw data approaches or visual approaches without the autoflight system.
Cheers

Welcome to aviation.se! Please consider using a linebreak here and there to facilitate reading. Also, please be aware that salutations are not needed here, and usually are considered distracting.


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How do multiple-disc brakes work?
Multiple disc brakes uses stators & rotors to brake?
How do they work?
(Source)

The overall answer would be the stack of discs is pressed by the pressure plate using a fluid and friction slows the rotors. This is explained on the original site. Could you clarify which part you don't understand,  Is this the friction part, the fluid part?...

Exactly as mins said, this works just the same as a single disc brake, just with more discs.

I am voting NOT to close this question as I believe the theory and function of aircraft mechanical systems to be on topic here. However, if you have an opinion on the quality of this question—for example it is "especially useful" or it displays "no-effort-expended"—I would encourage you to indicate this with an up or down vote.

A disc brake works in a very similar way to the brakes on a bicycle. The wheel rim on the bicycle can be considered to be similar to one of the discs in an aircraft brake unit. When the brake is applied on a bicycle the callipers squeeze the brake pads against the rim, the friction slows the rim/wheel.
A typical aircraft brake pack consists of several discs which are keyed to the inside rim of the wheel and rotate with the wheel, there are also several discs which are keyed to the stationary axle, these discs are interleaved and form a pack. The rotating discs in the wheel rim are squeezed against the stationary discs on the axle by hydraulic pressure using several pistons spaced around the discs, (like several calipers might be spaced around the wheel rim of a bicycle if they were required). The resultant friction slows the wheel and consequently the aircraft. Incidentally the friction energy is converted to heat during the braking.


text:
I live directly south in the line of a north-south landing strip of a low-traffic airport. What should I know?
There is an airport in my city that is relatively low traffic. It has a landing strip that runs north-south, and it looks like if you were to go ten miles straight south from that landing strip, you'd pass over my property.
The noise is infrequent and quiet enough that it isn't very bothersome, but I'm more or less in the flight path. But I'm ten miles away in its airpath. What should I be concerned about?

Should I be concerned about jet fuel exhaust or anything as far as my personal health and safety are concerned?
Is there any precaution I should take in the event that aircraft were to fall into my property?

What else should I know?

Don't be concerned about exhaust, you get a much higher dose spending 10 minutes on a busy street. The only precaution you should take if an aircraft fell on your property would be to call the authorities. Do not move the aircraft, even after everybody leaves.

If you have young kids, it's probably not a good idea to show them Donnie Darko.
Appart from this, the risks are sufficiently remote so that you don't need to think about it.

Well, if the Queen of England can stand living about 10 miles west of one of the world's busiest airports...

"precaution I should take".  What do you mean?  A precaution implies prevention.  Are you asking what you can do to stop an aircraft crashing onto your property or what you can put in place to deal with the aftermath?

What should you know?? Well the wet hire & instructor rates of course. Go learn to fly!

Take a walk to the airport and ask.  How long you been living there?  How long airport been there?